1. Field of the Invention
The present invention relates to floating type magnetic head devices provided for hard disk apparatuses or the like. In particular, the present invention relates to a magnetic head having a slider, and a flexure which supports the slider and which is electrically connected thereto with a conductive resin film.
2. Description of the Related Art
FIG. 4 is a partial side view showing the structure of a conventional magnetic head device for a hard disk apparatus. This magnetic head device is composed of a slider 1, and a supporting member 2 which supports the slider 1.
The slider 1 is formed of a ceramic material or the like. A thin-film element 4 is provided on a trailing end B of the slider 1. The thin-film element 4 includes an MR head (reading head) for reading magnetic signals by detecting a leakage magnetic field, using a magnetoresistance effect, from a recording medium such as a hard disk, and an inductive head (writing head) comprising a coil is formed by patterning.
The supporting member 2 is composed of a load beam 5 and a flexure 6. The load beam 5 is formed of a leaf spring material such as stainless steel, and has a bent section 5a on each side of the front portion thereof so as to have rigidity. A predetermined resilient force can be obtained at the base end of the load beam 5 where the bent section 5a is not formed.
A spherical pivot 7 (which protrudes downward in the figure) is formed in the vicinity of the front portion of the load beam 5, and the slider 1 abuts against the pivot 7 with the flexure 6 provided therebetween. The flexure 6 is formed of a leaf spring such as stainless steel. The flexure 6 includes a fixed section 6a and a tongue 6. A step 6c connects the fixed section 6a to the tongue 6b. 
As shown in FIG. 4, the slider 1 is bonded to the lower surface of the tongue 6b with a resin adhesive 20. This resin adhesive 20 is formed of, for example, a thermosetting epoxy resin adhesive. A conductive pattern (not shown in the figure) is provided on the rear side of the tongue 6b. In addition, an electrode terminal section (not shown in the figure), formed of a thin film extending from the thin-film element 4, is provided on the trailing end B of the slider 1. At the junction between this conductive pattern and the electrode terminal section, a joint 9 is formed by ball bonding using gold (Au) or the like. Furthermore, the joint 9 is covered with a reinforcing resin film 10, which provides protection for the joint 9.
A fillet-shaped conductive resin film 21 is formed between the leading end A of the slider 1 and the tongue 6b. This conductive resin film 21 is provided to secure the electrical connection between the slider 1 and the flexure 6, and to dissipate static electricity in the slider 1 to the supporting member 2 side.
The upper surface of the tongue 6b abuts against the pivot 7 provided on the load beam 5. This permits the slider 1 bonded to the lower surface of the tongue 6b to freely change attitude, by means of the resilience of the tongue 6b, with the apex of the pivot 7 serving as a fulcrum.
This conventional magnetic head device is used for a so-called xe2x80x9cCSSxe2x80x9d (Contact Start Stop) type hard disk apparatus or the like, and when the disk D stops, an air bearing surface (i.e., a floating surface, hereinafter referred to as an ABS) 1a of the slider 1 is brought into contact with a recording surface of the disk D. The slider 1 of the magnetic head device is urged toward a disk D by the resilient force of the base end of the load beam 5. When the disk D starts, an airflow occurs between the slider 1 and the surface of the disk D in the direction of the disk movement, and the slider 1 is lifted above the surface of the disk D by a short distance xcex42 (spacing) because of the lifting force caused by the airflow.
While the slider 1 is lifted (as shown in FIG. 4), the leading end A of the slider 1 is lifted higher above the disk D than the trailing end B. While maintaining this lifting attitude, magnetic signals are either detected from the disk by the MR head of the thin-film element 4, or are written on the disk by the inductive head.
A process for manufacturing the magnetic head device described above generally comprises the steps of bonding the upper surface of the slider 1 to the lower surface of the tongue 6b of the flexure 6 with the resin adhesive 20, electrically connecting an electrode of the flexure 6 to a pad portion of the slider 1 with the joint 9 (such as a gold ball), and inspecting the electrical characteristics of the magnetic head device.
In the step of inspecting the electrical characteristics described above, the inspection is performed under conditions almost identical to actual usage conditions. That is, for example, the ABS (floating surface) 1a of the slider 1 is in contact with the recording surface of the disk D, the disk D is then started, and subsequently, the slider 1 is lifted above the surface of the disk D by a short distance xcex42 (spacing). As a result, the slider 1 may be electrified by friction with the disk D or the like, and a potential difference between the slider 1 and the disk D may be generated.
This problem may also occur in other types of magnetic head devices. For example, in a load/unload type head, a recording medium and the slider are theoretically not brought into contact with each other. However, they are brought into contact with each other under certain conditions (e.g., contacts can occur while the disk rotates), and as a result, a potential difference between the slider and the recording medium may be generated as in the case of the CSS type device.
In the magnetic head described above, it has been generally believed that electrical conduction in the conductive resin film 21 is ensured by dielectric breakdown which occurs between particles of the conductive filler compounded with the resin. Accordingly, the electrical conduction cannot be obtained if a voltage greater than a predetermined threshold value is not applied. That is, electrical conduction between the slider 1 and the flexure 6 cannot be ensured until the voltage applied thereto exceeds the predetermined threshold value.
Consequently, when the threshold value is larger than an electrostatic breakdown voltage in which electrostatic damage to an MR element or the like occurs, electrical conduction between the slider 1 and the flexure 6 cannot be ensured, and when the slider 1 is electrified, the charges therein cannot be dissipated to the supporting member 2 side via the conductive resin film 21. As a result, there has been a problem in that electrostatic breakdown of a thin-film element 4 (such as an MR head) may occur when this electrified slider 1 is brought into contact with metal or the like.
In addition, as shown in FIG. 4, the trailing end B of the slider 1 is rigidly bonded to the tongue 6b of the flexure 6 by the joint 9 formed by ball bonding. Furthermore, as shown in FIG. 4, the conductive resin film 21 is provided between the leading end A of the slider 1 and the tongue 6b of the flexure 6.
However, in conventional magnetic head devices, the flatness of the ABS (floating surface) 1a of the slider 1 can easily vary. In other words, the crown height (which will be described later) easily varies, and hence, it has been very difficult to maintain a constant spacing xcex42. The reason the flatness of the ABS 1a of the slider 1 (i.e., the crown height) can easily vary is thought to be because the conventional conductive resin film 21 provided between the slider 1 and the lower surface of the tongue 6a of the flexure 6 contains a rigid resin such as a thermosetting epoxy resin as an adhesive (binder).
In addition, since the slider 1 has a coefficient of thermal expansion different from that of the flexure 6, when the conductive resin film 21 provided between the upper surface of the slider 1 and the lower surface of the tongue 6b is rigid, thermal stress generated by the difference in coefficient of thermal expansion between the tongue 6b and the slider 1 may affect the slider 1. As a result, deformation of the bonding position of the slider 1 can occur because of the influence of the conductive resin film 21.
Since the flexure 6 has a larger coefficient of thermal expansion than the slider 1, the ABS 1a of the slider 1 is deformed in a low temperature region to be convex in relation to the disk D, and the spacing loss is increased, thereby resulting in a decrease in output. In contrast, the ABS 1a of the slider 1 is deformed in a high temperature region to be concave in relation to the disk D. This may result in the trailing end B of the slider 1 colliding with the surface of the disk D, and hence, the minimum floating amount (spacing) cannot be maintained in some cases.
In consideration of the problems described above, the present invention was made in order to achieve at least the following objects: (1) to prevent the generation of electrostatic breakdown of a magnetic head device; (2) to decrease a conduction starting voltage for electrical conduction of a conductive resin film; (3) to improve electrical conduction properties of the conduction resin film; and (4) to prevent the degradation of floating properties of a slider caused by the formation of the conductive resin film.
A magnetic head of the present invention comprises a slider having a thin-film element which performs at least one of writing and reading; a flexure bonded to the slider and having a tongue which is resiliently deformable; and a conductive resin film which electrically connects the slider to the flexure; wherein the conductive resin film has a conduction starting voltage of 2.0 V or less. Moreover, the conductive resin film preferably has a conduction starting voltage of 1.0 V or less.
According to the present invention, the conductive resin film may comprise a thermoplastic elastomer and conductive filler, and the conductive filler content may be 70 wt % or more. Moreover, the conductive filler content is preferably 80 wt % or more.
In addition, according to the present invention, the conductive resin film described above may have a durometer hardness of less than D-40. Moreover, the conductive resin film preferably has a durometer hardness of less than D-20.
In the present invention, when a voltage of 0.5 V is applied across the slider and the flexure, the resistance is preferably 1 Kxcexa9 or less. When a voltage of 0.1 V is applied across the slider and the flexure, the resistance is more preferably 1 Kxcexa9 or less.
Furthermore, in the magnetic head of the present invention, a voltage equal to or more than a conduction threshold voltage of the conductive resin film may be applied across the slider and the flexure beforehand. In the step described above, the voltage applied beforehand is approximately 2 to 5 V, and is more preferably approximately 3 to 4 V.
In the magnetic head of the present invention, since the conduction starting voltage at which the slider and the flexure are electrically connected to each other is set to 2.0 V or less, or preferably 1.0 V or less, even when the slider is electrified, the charges can be smoothly dissipated to the flexure at the conduction starting voltage described above, and hence, electrostatic damage to the thin-film element used for writing and/or reading can be prevented.
When a voltage is applied to a conductive resin film composed of a thermoplastic elastomer and conductive filler compounded therewith, and when the voltage exceeds a predetermined threshold value, dielectric breakdown occurs between particles of the conductive filler, and hence, electrical conduction of the conductive resin film can be ensured. In the case described above, the conduction starting voltage means the threshold voltage described above.
In the present invention, as the thermoplastic elastomer, an elastomer primarily composed of, for example, an acrylic-based, a polyurethane-based, a polyester-based, or a nylon-based thermoplastic resin may be used. A silver-based, copper-based, or gold-based filler may be used, for example, as the conductive filler.
In the present invention, when the conduction starting voltage of the conductive resin film is set to more than 2.0 V, a potential difference of 2 V or more is generated between the slider and the medium due to the friction therebetween, and in addition, when the spacing xcex41 approaches ten nm, the recording area of the medium may be adversely affected by local discharge generated between the slider and the medium, or electrostatic damage to the thin-film element provided on the slider may easily occur. Accordingly, it is preferable that the conduction starting voltage be set to not more than 2.0 V.
In addition, in the case in which the conduction starting voltage of the conductive resin film is set to more than 1.0 V, and because it is expected that future technical developments will result in a spacing xcex41 of 10 nm or less, or that the resistance against static electricity of a thin-film element provided on the slider will decrease, and hence, electrostatic damage cannot be reliably prevented. Accordingly, it is preferable that the conduction starting voltage be set to not more than 1.0 V.
The durometer hardness of the conductive resin film is preferably set to less than D-40 and is more preferably set if to less than D-20. Accordingly, the change in flatness of the ABS (hereinafter referred to as xe2x80x9cadhesive deformationxe2x80x9d), which occurs when the conductive resin film 11 is formed between the slider and the flexure, can be reduced.
The durometer hardness in the present invention is a value obtained by a measurement method in accordance with JIS-7215 (Japanese Industrial Standards) or the like and is generally used as an index of hardness of a coated resin film. In order to measure the durometer hardness, an indenter of a specified measuring device is pressed on a coated resin film, and the durometer hardness is determined in accordance with the depth to which the indenter enters the coated resin film. A high durometer hardness means a harder and more rigid coated resin film.
When the durometer hardness of the conductive resin film is set to D-40 or more, and when the resin is cooled to room temperature after heat curing, the strain generated due to the difference in coefficient of thermal expansion between the slider and the flexure cannot be absorbed by the deformation or elongation of the conductive resin film, and the strain adversely affects the slider as a thermal stress, thereby changing the flatness of the ABS. Accordingly, it is preferable that the durometer hardness of the conductive resin film be not more than D-40.
In addition, when the durometer hardness of the conductive resin film is set to D-20 or more, because of an anticipated future decrease in the size of the slider (0.3 mm to 0.2 mm), the rigidity of the slider itself is decreased, and hence, the thermal stress described above easily affects the slider, whereby the flatness of the ABS can easily vary. Accordingly, it is preferable that the durometer of the conductive resin film be not more than D-20.
When the durometer hardness of the conductive resin film is set as described above, the strain generated between the slider and the flexure due to the difference in coefficient of thermal expansion therebetween can be absorbed, and in addition, a very flexible conductive resin film can be used to reduce the internal stress generated due to the shrinkage thereof during curing. Accordingly, when one side (trailing side) of the slider is rigidly bonded to the flexure, even though a thermal stress is generated due to the difference in coefficient of thermal expansion between the slider and the flexure, the change in flatness of the ABS (floating surface) of the slider or the change in crown height can be prevented.
In the present invention, it is preferable that the conductive resin film be composed of a thermoplastic elastomer and conductive filler compounded therewith, and that the conductive filler content be set to 70 wt % or more. In addition, the conductive filler content is more preferably set to 80 wt % or more. Accordingly, both the conduction starting voltage (that is the threshold value described above) and the durometer hardness of the conductive resin film can be controlled in the appropriate ranges.
When the conductive filler content is set to less than 70 wt %, the resistance at a measurement voltage of 2.0 V becomes 1 Mxcexa9 or more or infinite, the charges generated in the slider due to the friction with a medium cannot smoothly be dissipated to the flexure, and damage to a recording area of the medium caused by local discharge or electrostatic damage to a thin-film element provided on the slider can easily occur. Accordingly, it is preferable that the conductive filler content be not less than 70 wt %.
In addition, when the conductive filler content is set to less than 80 wt %, since it is expected that the spacing between the slider 1 and the media will be decreased by future technical developments, and that the resistance against static electricity of the thin-film element provided on the slider will decrease, the electrostatic damage described above cannot be reliably prevented. Hence, it is preferable that the conductive filler content be set to not less than 80 wt %.
In the magnetic head of the present invention in which the resistance is set to 1 Kxcexa9 or less at a measurement voltage of 0.5 V applied across the slider and the flexure, even when the slider is electrified due to the friction with a medium, and a potential difference of 0.5 V or more is generated between the slider and the medium, the charges in the slider can be smoothly dissipated to the flexure via the conductive resin film because of the low resistance between the slider and the flexure described above. Hence, electrostatic damage to the thin-film element used for writing and/or reading caused by the electrified slider can be prevented.
In addition, in the magnetic head of the present invention in which the resistance is set to 1 Kxcexa9 or less at a measurement voltage of 0.1 V applied across the slider and the flexure, even when the slider is electrified due to the friction with a medium, and a potential difference of 0.1 V or more is generated between the slider and the medium, the charges in the slider can be smoothly dissipated to the flexure via the conductive resin film because of the low resistance between the slider and the flexure described above. Hence, electrostatic damage to the thin-film element used for writing and/or reading caused by the electrified slider can be prevented.
In order to form a magnetic head in which the resistance is set to 1 Kxcexa9 or less when a voltage of 0.1 to 0.5 V is applied across a slider and a flexure, as described above, first, a magnetic head having a slider provided with a thin-film element for writing and/or reading, a flexure bonded to the slider and having a tongue which can be resiliently deformed, and a conductive resin film electrically connecting the slider to the flexure is prepared. Subsequently, a voltage of approximately 2 to 5 V, which is larger than the threshold voltage, is applied, or a voltage of approximately 3 to 4 V is preferably applied, across the slider and the flexure before the magnetic head is used, whereby a magnetic head having the properties described above can be formed.
Concomitant with the trend toward miniaturization and higher performance of thin-film elements such as MR heads because of increases in magnetic recording density, with the threshold voltage at which the electrostatic breakdown of the thin-film element occurs being further decreased, the magnetic head of the present invention can nevertheless satisfactorily withstand the condition described above, and electrostatic damage to the thin-film element can be reliably prevented.